It is known in the art that the esterification of condensed castor oil fatty acids with polyglycerol may result in a potentially powerful water-in-oil emulsifier that may be used by the food industry, for example, in tin-greasing emulsions and as an emulsifier with lecithin to produce chocolate covertures and block chocolate.
As an emulsifier, PGPR has a low hydrophilic-lipophilic balance (“HLB”) value and finds utility in water in oil emulsions such as low fat table spreads because of this property. PGPR has been used in foods, drugs and cosmetics. For example, PGPR is an emulsifier approved in many countries for use as an additive for chocolate.
One of PGPR's desired physical behaviors is the physical separation of solids in a slurry. Therefore, additional applications of PGPR includes its use in paints, coal slurries and other high solids compositions that typically require reduction in low shear viscosity or reduction in yield value of pseudo-plastic materials.
PGPR has been reported in several scientific articles and patents. For example, U.S. Pat. Nos. 4,590,086 and 4,971,721 (both to Takahashi, et al.) describe processes utilizing PGPR for the production of water-in-oil-in-water emulsions for medicines, cosmetics, foods, etc. The disclosures of these two patents are incorporated herewith by reference in their entirety.
PGPR has been the subject of a previous submission to the Food and Drug Administration of the United States of America as a part of GRAS Notification, No. 0009, for use as a rheology modification agent in a molten chocolate mass. In GRAS Notification, No. 0009, PGPR is defined as an interesterified polymer of polyricinoleic acid and polyglycerol.
Polyricinoleic acid is a polymer that can be created by the self-condensation of a 12-hydroxy, 9-octadecenoic acid fraction of fatty acids obtained from castor oil. The condensation reaction is typically carried out by heating castor oil fatty acids to about 200° C., with or without catalyst, and removing water of reaction. Acceptable catalysts are those known in the art and include acids such as phosphoric acid, bases such as sodium hydroxide and lipase enzymes, all of which are currently used to interesterify food grade fats and oils.
Polyglycerol can be obtained either by the controlled polymerization of substituted propyl-1, 2-oxyrane, or through the direct condensation of glycerin under highly basic conditions.
Polyricinoleic acid and polyglycerol can then be interesterified through esterification mechanism to form PGPR.
A full description of PGPR is given in the Fiftieth Edition of the Food Chemical Codex (FCC), published by the Institute of Medicine. Specifications and analytical chemistry associated with PGPR as a food additive are provided for in this reference. The FCC monograph, “Polyglycerol Polyricinoleic Acid,” is hereby incorporated by reference in its entirety. The key specifications of PGPR suitable as a food additive listed in the FCC are as follows:
Acid Value:Not greater than 6.0;Hydroxyl Value:Between 80 and 100;Iodine Value:Between 72 and 103;Saponification Value:Between 170 and 210; andRefractive Index:Between 1.463 and 1.467 @ 65° C.
All of the specifications listed above with the exception of refractive index are weight average analysis and do not indicate specific structural characteristics of PGPR. Taken on the whole, however, these weight average related specifications do indicate correct chemical structure, but with limited accuracy. Refractive index, however, is directly indicative of final chemical structure; e.g., if the oligomer distribution of PGPR is not correct or distributed differently on the polyglycerol backbone, the refractive index measurement will not comply with the specifications as described above.
In summary, the conventional process for making PGPR, as described in the GRAS Notification No. 0009, generally includes the steps of (1) condensing glycerin to make a polyglycerol; (2) condensing ricinoleic acid to make a polyricinoleic acid; and (3) interesterifying the two polymers to make the final PGPR product.
One problem with this conventional process is that the step of polymerization of ricinoleic acid is complicated by the fact that there is a requirement to follow the refractive index of the mixture while polymerization of ricinoleic acid and/or interesterification of polyglycerol and polyricinoleic acid is under way and to stop the reaction when the key value is indicated by the analysis. The refractive index test is not easily established in a manufacturing facility because the instrument is delicate, requires precise calibration and requires a circulating temperature bath set to a particular temperature, e.g., 65° C. It is therefore difficult to run the refractive index test at the kettle, and this often requires that the instrument be used in a laboratory setting, usually in a quality control laboratory. If one uses refractive index as the guide, one needs to run samples to the laboratory, and place them in the laboratory queue. This is both time consuming and inconvenient. Moreover, the refractive index requires a high degree of technical training and precision.
The three-step conventional process also reduces efficiency of production and adds cost to the product. Therefore, there is a need for a more economical and simplified method for manufacturing PGPR.
Further, in the conventional process, there is a tendency to produce compositions of darker color. This is most likely due to the added processing steps of preparing two separate ingredients, each having its own cycle of heating and cooling, along with the additional handling associated with the manufacture of each ingredient. As a result, there is a need for a method that can produce noticeably lower color end product, such as a clear yellow liquid rather than an amber liquid.